This invention relates to apparatus and a process for cooling the bottom of a mold (usually in practice at the top of the mold car) used in the electroslag remelting (ESR) process. More particularly it relates to a spray cooling of the bottom of ESR molds whereby butt cracking which heretofore existed in the bottoms of ingots produced by the ESR process is eliminated.
The ESR process is used for producing high quality speciality steels and non-ferrous alloys by the fusing of metal from the bottom of a consumable electrode received in a blanket of slag or flux, such metal being refined as it passes through the molten slag or flux. This is generally accomplished by suspending the consumable electrode within a water cooled copper or steel mold with a layer of molten slag disposed in the bottom therein. The slag acts as a conductor for an electric current passing between the consumable electrode and the starter plate or stool which is usually at the bottom of the mold. The mold usually has an open bottom and is supported on the starter plate by a water cooled base which may also be considered part of the operative mold. This base may be the top of a mold supporting car. The process commences when a layer of molten slag is received in the bottom of the mold and the top part of the electrode is received in the molten slag. Current then passing through the electrode and molten slag heats the electrode and droplets of metal fusing off the electrode's lower end fall through the slag to the bottom of the mold where a pool of molten metal forms and solidifies upward from the bottom of the mold thus forming an ingot. A refining action takes place on the molten metal as it passes through the molten slag and, as the electrode is progressively consumed, refined metal builds up from the bottom of the mold to form the ingot. The molten slag floats on the pool of refined metal and remains in contact with the lower end of the consumable electrode with the refining process being continued until the electrode is consumed or substantially consumed.
In the production of steel by the ESR process it has been a usual practice to control the rate of cooling of the molten metal by the circulation of water in the walls of the mold and through the bottom of the mold or mold car as the refined ingots are being formed. Although this practice has been very effective in the production of high quality steel, certain difficulties have been encountered during the initial forming phase of the ingot. One such problem has been the formation of butt cracks appearing in the bottom of the ingots. Also any leakage which might occur from the cooling water could lead to introduction of hydrogen into the ingot and result in hydrogen embrittlement of the ingot steel.
In seeking a solution to the leakage problem, it is the concept of the inventor that adequate cooling might be obtained by a controlled spray system rather than solid fluid cooling. The use of a spray to cool an ESR mold is not new, as such, such being disclosed in a prior art patent to Hopkins U.S. Pat. No. 2,300,670. Also the technique of using a spray for cooling the bottom of an ingot mold is not new, as such, as evidenced by U.S. Pat. No. 1,298,825 of Tebbetts. Other prior art patents involving a spray for cooling molds include the patent to York U.S. Pat. No. 1,551,277, the patent to Leary, U.S. Pat. No. 1,753,380 and the patent to Woodburn, U.S. Pat. No. 3,590,904.